A bacterium of great clinical relevance is the gram-positive bacterium Staphylococcus aureus. It is one of the most frequent causes of nosocomial infections (infections transmitted in hospital), the spread of which is difficult to control because of the occurrence of various forms of antibiotic resistance (for example, resistance to methicillin and vancomycin). Staphylococcus aureus is also one of the most frequent causes of food poisoning, which is generally caused by enterotoxins. The frequent occurrence of Staphylococcus aureus in foodstuff products therefore requires a regular investigation of potentially contaminated products. Conventional microbiological methods for the detection of Staphylococcus aureus are very time-consuming (at least 4 days). There is therefore a great need for alternative methods, by means of which the presence of Staphylococcus aureus can be diagnosed rapidly and reliably in the course of the production process (from the raw materials to the finished product).
A number of new methods for routine use in the detection of microorganisms have been developed in recent years. These include immunological methods based on the use of polyvalent or monoclonal antibodies, and methods in which nucleic acid probes are used for detection by means of hybridisation to organism-specific nucleic acids. Further methods described are those based on amplification of a specific nucleic acid, with or without a subsequent confirmation reaction by nucleic acid hybridisation.
Methods used for the amplification of nucleic acids are, for example, polymerase chain reaction (PCR) [U.S. Pat. Nos. 4,683,195; 4,683,202; and 4,965,188], ligase chain reaction [WO Publication 89/09835], “self-sustained sequence replication” [EP 329 822], the “transcription based amplification system” [EP 310 229] and the Qβ RNA-replicase system [U.S. Pat. No. 4,957,858].
The nucleic-acid-based methods mentioned are so sensitive that, unlike in conventional microbiological methods, the tedious process of increasing the quantity of the microorganism to be detected from the sample to be investigated is unnecessary. A test for the presence or absence of the microorganism in question is therefore generally concluded within one working day when using the nucleic-acid-based methods mentioned. This constitutes a considerable time saving, in particular when several days to several weeks are needed for detection by conventional methods.
A number of rapid tests have recently been developed by means of which the presence of Staphylococcus aureus can be significantly shortened. These include coagulase tests, various agglutination tests, TNase tests (enzyme activity, monoclonal antibodies), DNA hybridisation tests and PCR tests [for an overview, see BRAKSTAD and MAELAND, (1995), APMIS 103, 209–218]. PCR tests are superior to the other methods in terms of speed and specificity. The PCR tests described hitherto for the specific detection of the Staphylococcus aureus species are based on the gene for thermostable nuclease [nuc, Brakstad et al., (1992), J. Clin. Microbiol. 30, 1654–1660] or on a regulator gene essential for methicillin resistance (femA), which is specific for Staphylococcus aureus [Ünal et al., (1992), J. Clin. Microbiol. 30, 1685–1691; Vannuffel et al., (1995), J. Clin. Microbiol., 33, 2864–2867]. Using those PCR systems, it has been possible to detect all the investigated species of Staphylococcus aureus. It is unclear, however, whether it is also possible to detect coagulase-negative strains of the species Staphylococcus aureus using those PCR systems.
The aim of the present invention was to establish a PCR system, the use of which as primers and/or probes ensures as complete detection as possible of all the representatives of the species Staphylococcus aureus. 
Depending upon the size of the group of microorganisms to be detected and on the evolutionary relationship of microorganisms to be delimited (not to be detected), detection based on differential DNA sequences requires very comprehensive preliminary work in order to find suitable DNA sequences having the desired specificity in each case. The invention described herein relates to DNA sequences by means of which the rapid detection of bacteria of the genus Staphylococcus, especially of Staphylococcus aureus, is possible.